As prostate cancer has recently become the most widely diagnosed form of cancer in United States' males, clinicians are expected to seek more effective treatment modalities. One of these may be hyperthermia as an adjunct to radiation and chemotherapy. The main limitation to this mode of therapy has been the lack of effective heating equipment for the prostatic region.A novel two-applicator microwave heating system has been proposed for heating the prostate. Two applicators inserted transurethrally and transrectally would provide a multiple antenna array around the prostate tumor.Choked microwave antennas in the applicators would limit heating to the prostatic region. Air cooling of the applicator's surfaces would prevent damage to the rectal mucosa and the urethelium. Phase modulation among the antennas would allow uniform heating of the entire prostate. In Phase I, the applicants have proposed to design, construct, and test such an antenna array system. Experiments to test system efficacy would be performed in tissue equivalent phantom to determine power deposition profiles and steady-state temperature profiles. Modifications to improve system performance would be made as necessary. The goal of Phase I is to develop a system in preclinical animal experiments and clinical trials in Phase II.